This paper addresses the problem of planning two fingered grasps of unmodelled 3D objects using visual information. A family of simultaneous, interacting contour trackers is used to pick the top object off a pile, viewed from a camera on the end of a robot arm. Then a closed contour localises the silhouette of the chosen object. Geometric information is obtained from the analysis of image motion as the robot executes deliberate world motions around its vantage point. This is used to guide the selection of new vantage points in search of a view that contains a more favourable grasp on the new rim (the surface curve that projects to the silhouette). In this way, costly global reconstruction of object surfaces is avoided and planning is coupled with sensing in an efficient manner.>

The authors discuss establishing a relationship between symmetry and two-fingered grasping of planar contours. Visual representations are chosen to meet the requirements of specified tasks such as object recognition or stereoscopic matching. When vision is regarded as a haptic sense, a new operational description is called for in support of dextrous manipulation. In the context of two-fingered grasp, an appropriate description can be constructed in terms of local reflectional and rotational symmetry. Related to symmetry-based representatons that have been used in pattern and object recognition, its structure is determined not heuristically, but precisely, by the nature of the grasping task. Its value is demonstrated by its incorporation into the control of a robot that can manipulate objects under visual guidance.>